The purpose of the present investigation is to study the aryl hydrocarbon hydroxylase (AHH) and the covalent binding of (-)r-7,t-8-dihydroxy-7,8-dihydrobenzo(a)pyrene to DNA in control, phenobarbital and 3-methylcholanthrene induced rabbit liver microsomes and with purified forms of cytochrome P-450 isolated from phenobarbital and 5,6-benzoflavone induced rabbit. The in vitro effect of 7,8-benzoflavone, butylated hydroxytoluene and ascorbic acid on these two metabolic activities will be evaluated.